Immersion in a foreign country (or immersion in horny foreign men in a topless bar) provides ample and unavoidable opportunities to learn an oral 2nd language. My poorly spoken Chinese has been acquired in that manner.

But Chinese students in China do not have that resource unless they live in certain neighborhoods in Beijing or Shanghai.

For a Chinese student, two academic years of oral English with China's most talented FT (me) is not as productive as two months stranded in Boise Idaho, Nottingham England or Ottawa Canada.